[Stricture of oxygen outlet of the central piping identified by a decrease in the oxygen supply pressure into the anesthesia machine].

We experienced an incident of the stricture caused by the degradation of an O-ring in the oxygen outlet of the central piping. The event was identified by the intermittent decrease of the central piping oxygen supply pressure into the anesthesia machine. In this case, pressure was judged normal by periodical checking. But the malfunction became clear when the parts of outlet were replaced, because similar incidents frequently had occurred. The cyclical rhythm of the declining oxygen supply pressure means that oxygen supplies decreases with the increase of oxygen consumption, and it may be a sign of serious malfunction. Therefore, it is necessary to check the pressure deviations under use of high-flow oxygen.